The present invention relates to a vehicle tire having a unidirectional tread pattern being capable of reducing pattern noise during running.
In general, vehicle tires such as pneumatic tires are provided with various tread patterns to secure wet grip. Especially, unidirectional tread patterns symmetrical about the tire equator are widely employed in passenger car tires in recent years.
In such unidirectional tread patterns, edges of tread grooves, especially those of axial or bias grooves formed on both sides of the tire equator are liable to contact with the ground synchronously. As a result, running noise and so called pattern noise is liable to increase when compared with bi-directional tread pattern.
It is therefore an object of the present invention to provide a pneumatic tire which has a unidirectional tread pattern capable of improving the pattern noise.
According to the present invention, a vehicle tire comprises a tread portion provided with a unidirectional pattern, the tread portion provided with two circumferential grooves to divide the tread portion into two outer parts and a central part therebetween, the central part being substantially continuous in the tire circumferential direction and formed symmetrically about the tire equator, the outer parts provided with mirror-image patterns respectively, each of the mirror-image patterns formed by circumferentially repeating pattern units having an average circumferential length, and the mirror-image patterns of the two outer parts being circumferentially shifted from each other by a distance of from 0.15 to 0.25 times the average circumferential length.
Embodiments of the present invention will now be described in detail in conjunction with the accompanying drawings.